This invention relates to an actuator for a power fold mechanism of a rear view device for a vehicle, preferably for a motor vehicle. The invention also relates to a rear view device for a vehicle, preferably for a motor vehicle, having such an actuator installed.
In modern day vehicles, actuators employing shape memory alloys are utilized for retractably tilting rear view device housings of a vehicle, preferably of a motor vehicle. The rear view device housings in which back view elements are contained are commonly mounted on panels arranged on the front doors such that the rear view device housings project outwardly in a sidewise direction. During maneuvering the vehicle in narrow spaces, sensor means installed in the rear view device, or in some other location in the vehicle, can sense imminent danger to the rear view device, for example due to an imminent collision with a pillar or another vehicle, and can initiate tilting the rear view device housings so as to avoid the collision.
However, the actuators that are known in the prior art require rather generously spaced installation compartments for installing the actuators in the rear view device. This is mainly due to the wire lengths which could easily be 300 mm and more, i.e. depending on the mirror and/or vehicle type. One problem associated with storing long wires made of active material is that the wires will likely get destroyed when they are being bent or folded. A space saving solution for storing long wires made of active material is described in EP 2781743 A1. The prior art document suggests to wind a wire made of active material around a rotatably mounted actuator pin. The prior art actuator uses the so called “JoJo-effect”, i.e. when the wire consisting of active material is activated, e.g. by means of electricity, the wire shortens, and the actuator pin starts to rotate about its own axes which causes the rear view device housing that is mechanically coupled to the actuator pin to fold in.
Winding up a wire consisting of active material around an actuator pin can be a space saving solution, but since the wire is wound around the surface of the actuator pin, frictional forces will arise that decrease the overall efficiency of the actuator. Also, by winding up a wire consisting of active material, the maximum folding sizes of the utilized wire need to be taken into account when designing the actuator, so that the wire does not get destroyed by over-bending the wire during operation. Further, only wires consisting of active material that have a rather thin diameter allow to be wound up, since wires having a larger diameter cannot be sufficiently bent without getting destroyed. However, the maximum tension of a wire consisting of active material increases with the diameter of the wire. Therefore, the prior art actuator using the JoJo-effect can only move rear view device housings that are sufficiently lightweight.
Therefore, the invention aims at providing an actuator for a rear view device of a vehicle that overcomes the above mentioned problems. Namely, it would be desirable to provide an improved interaction between an active material actuator and an actuator pin.